Hydrogenation of adiponitrile

ABSTRACT

Process for the catalytic hydrogenation of adiponitrile at elevated temperatures and pressures in the presence of a catalyst derived from an iron compound in granular form which has been activated with hydrogen at a temperature not exceeding 600* C.

United States Patent Kershaw et a1. 5] Oct. 3, 1972 [S4] HYDROGENATIONOF ADIPONITRILE [56] References Cited [72] inventors: Bernard JohnKershaw; Maurice UNITED STATES PATENTS George Pounder; Kenneth RossWilkins, all of Brockville, O ta i 3,056,837 10/1962 Steeman ..260/583 KCanada 3,152,184 10/1964 bevering............260/583 K X [73] Assigneeza I. d Pom de Nemom and C 2,956,075 10/1960 Boffa et a1 ..260/583 K Xpany, wllmmgton, Del. E .nehdxwis Guns [22] Filed: May 7, 1970 AssistantExaminer-Richard L. Raymond [2]] App. NO: 35,573 Attorney-Wiiham A.Hoffman F A h Pri Du [57] ABSTRACI ti '1 ta [30] pp ca on on y Processfor the catalytic hydrogenation of adiponitrile July i l, Canada atelgvated temperatures and pressures in the presence of a catalystderived from an iron compound in granu- [52] US. Cl ..260/583 K, 252/4591 f which has been activawd with hydrogen at a [5 1 Int. Cl ..C07c 85/12temperature not exceeding 00 c [58] Field of Search ..260/583 K 7Claims, No Drawings HYDROGENATION OF ADlPONITRlLE The present inventionrelates to the catalytic hydrogenation of adiponitrile and moreparticularly to an improvement in the preparation of hexamethylenediamine by the hydrogenation of adiponitriie in the presence of acatalyst with improved service life.

Hexamethylene diamine is a well-known compound which may be preparedcontinuously on a commercial scale by catalytically hydrogenatingadiponitrile in the presence of ammonia. A principal use ofhexamethylene diamine involves condensing it with dibasic acids toproduce polyamide, and in manufacturing these polyamides, especiallythose wherein hexamethylene diamine is reacted with adipic acid toproduce polyhexamethylene adipamide.

In the continuous production of hexamethylene diamine by the catalytichydrogenation of adiponitrile, a high purity adiponitrile is necessary;small traces of impurities present may poison the hydrogenation catalystand so reduce the catalysts activity and shorten its usable service lifemarkedly. Adiponitrile is frequently synthesized from adipic acid andammonia in the presence of dehydrating catalysts such as the oxides ofphosphorus, silicon, tungsten, titanium, molybdenum and the like. Sidereactions occur when adipic acid and ammonia are reacted togetherresulting in the formation of various impurities. it is these impuritieswhich, if not removed, tend to have a deleterious effect upon theefficiency, yield and life of the hydrogenation catalyst in thesubsequent hydrogenation of the adiponitrile to hexamethylene diamine.Before the adiponitrile may be catalytically hydrogenated for commercialproduction of hexamethylene diamine, thorough purification of thestarting materials has thus, in the past, been essential.

Many catalysts have been suggested for the hydrogenation of thoroughlypurified adiponitrile. Most frequently, nickel or cobalt or mixturesthereof (usually precipitated upon a finely divided carrier) and alsoRaney catalysts have been used for the hydrogenation reaction. lroncatalysts made by a melting technique and activated by means of alkalimetals have also been suggested. Quite often, the hydrogenation ofadiponitrile has been carried out in liquid ammonia in the presence ofhighly activated nickel or cobalt catalysts at temperatures of between90C. and 150C. if the temperature is raised far above [50C, formation ofunderisable hexamethyleneimine is considerably intensified. Attemperatures below 90C., the activity of these conventionalcatalysts istoo low.

The conventional nickel and cobalt catalysts are frequently prepared bydissolving out of aluminum from the aluminum alloys of the metals bymeans of caustic soda solution or by precipitation of the hydroxides onsuitable carriers and subsequent reduction. The production of highlyactive catalysts is thus difficult, complicated and requires great care.

Although many improvements have been effected in commercial continuoushydrogenation processes for the production of hexamethylene diamine,even the most sophisticated of these processes must be terminated atsome time because of detrimental reduction or loss in the ability of thecatalyst to aid or effect the required hydrogenation. This loss incatalyst activity occurs regardless of hydrogenation operatingtemperature at some point of time in the operation of the processdependent upon the operating conditions for the process and the amountof material which has been hydrogenated by any given catalyst as well asother factors.

It is an object of the present invention to prepare hexamethylenediamine by catalytically hydrogenating adiponitrile with the aid of animproved catalyst.

Another object is to provide an improved process for the preparation ofhexamethylene diamine by the catalytic hydrogenation of adiponitrilewith minimum formation of deleterious by-products such ashexamethyleneimine.

Yet another object is to provide an improved process for hydrogenatingadiponitrile to hexamethylene diamine in the presence of a catalystgiving improved yields and service life.

in accordance with the present invention, it has been discovered thatthese and other objects may be accomplished by hydrogenatingadiponitrile under controlled conditions of temperature and pressure inthe presence of ammonia and an iron compound in granular form which hasbeen activated by contact with hydrogen at temperatures not exceeding600C., said iron compound being capable ultimately of conversion intoelemental iron.

Accordingly, the present invention provides a process for the catalytichydrogenation of adiponitrile in the supercritical vapor phase tohexamethylene diamine at temperatures within the range to 200C. undersuperatmospheric pressures in the presence of a catalyst comprising aniron compound in granular form which has been activated by contact withhydrogen at temperatures not exceeding 600C., said iron compound beingcapable ultimately of conversion into elemental iron.

When the special catalyst for use according to the present invention isused in a fixed bed it is preferably used in relatively coarse granularform (having a particle size of from about one-tenth to one-twentiethinch). Much finer particle sizes tending to powders may be used if thecatalyst is used in a fluid bed or in a slurrytype reactor.

By super-critical vapor phase" is meant a condition in which thetemperature of the reactor is above the pseudocritical temperature ofthe reactor feed mixture.

The special catalyst for use according to the present invention has beendescribed and claimed in greater detail in an application filed on thesame day as the present application by .l.R.B. Boocock, F.T. Flood andBJ. Kershaw.

Reference to the copending application will show that it is preferred toactivate the catalyst with hydrogen at a temperature between 250C. and550C. Below 250C., activation proceeds at a rate inadequately fast formost commercial considerations. Activation above 600C. yields a catalystof activity inadequate for most practical purposes.

The catalyst may be obtained by reducing an iron oxide such as ferricoxide or ferroso-ferric oxide with hydrogen at temperatures in the rangeof from 250C. to 600C. until such time as the oxygen content of theoxide has decreased to less than 19 weight percent.

In another method the catalyst may be obtained by treating an iron oxidesuch as ferric oxide or ferrosoferric oxide with carbon monoxide attemperatures ranging from 200C. to 450C, preferably above 325C, forsufficient time to produce substantial amount of iron carbide and thenactivating the compound obtained by reducing it with hydrogen attemperatures in the range from 200C. to 600C.

For purposes of the present invention, it is preferred to treat ironoxide by heating it at about 400C. in a furnace under a stream of dryhydrogen for 40 to 50 hours using a relatively high flow rate for thestream of hydrogen. lf activation is allowed to proceed for too long aperiod, sintering of the catalyst may occur. It is desirable thatsubstantially no water be present during the activation treatment. Thecatalyst prepared in this manner will frequently show surface areas ofup to 30 to 35 sq.m./g. which is a substantial improvement in surfacearea over that of many of the commercially used hydrogenation catalysts.

The process of the present invention is particularly adapted forcontinuous operation. The temperature of the hydrogenation should beregulated within the range of from 100 to 200C. and accuratelymaintained during the continuous reaction by conventional proceduressuch as the regulation of flow rates and the temperature of thereactants. Temperatures between 105C. and 165C. are preferred forpracticing the process of the present invention in a continuous manner.Best results are obtained between about 1 C. and 150C. [t is preferredto practice the process of the present invention at about 340 atmpressure.

The process of the present invention may be conducted continuously formany days giving yields of up to 99 percent hexamethylene diamine. Itwill be appreciated that the degree of purity of adiponitrile used inthe process will determine the actual period for which the catalystremains effective. However, no special need be taken to purge mostcommercially synthesized adiponitriles of impurities, other thanZ-cyanocyclopentylideneimine and moisture, if the adiponitrile containsless than about 1 percent of impurities. (Whilst2-cyanocyclopentylideneimine has no deleterious effect on the catalyst,its hydrogenation reaction product is extremely difficult to remove fromhexamethylene diamine.)

The following Examples help to illustrate the present invention further.All mesh sizes are expressed as US. Standard Sieve sizes.

EXAMPLE 1 The following will compare the process of the presentinvention with a process of the prior art using a conventionalcommercially available cobalt oxide catalyst.

IRON CATALYST (A) 16.8 lb. moles of iron oxide (containing about 3percent by weight of alumina) having particle sizes from 0.055 to 0.093inches were charged into a cartridge tube having a diameter of 16inches. The cartridge was then inserted into a heater shell andpressurized to 90 psi with nitrogen. The iron oxide was then heated to350C, over a period of 3 hours, using preheated nitrogen. The nitrogenflow was stopped and replaced by a dry hydrogen flow of 92 lb. moles perhour that had been preheated to 500C; the temperature of the iron oxideincreased to 460C. This activation treatment was continued for a further48 hours and the product so obtained was allowed to cool to C. underhydrogen. Then the hydrogen flow was stopped and replaced by a stream ofnitrogen until the product had reached ambient temperature so yieldingthe iron catalyst.

COBALT CATALYST (X) Seven hundred and thirteen parts of cobalt oxide, inthe form of one-eighth inch pills, were divided into four approximatelyequal portions, each of which was placed in a furnace tube. Each portionwas heated in a stream of 167 volume parts per minute of helium to 250C.Hydrogen was then added to the gas stream at a rate of 17 volume partsper minute. After a further 2 hours the temperature was increased to350C. and the hydrogen flow to 40 volume parts per minute. Thetemperature was further increased to 400C. and the hydrogen flow wasgradually increased over a period of 4 hours to 167 volume parts perminute. After a further 15 minutes the helium low was decreased to 50volume parts per minute and the reduction allowed to continue for afurther 24 hours. The hydrogen flow was then decreased to 80 volumeparts per minute and the product allowed to cool to ambient temperature.The four portions were combined for use as the catalyst.

The following table sets out the operation conditions and results of tworuns, the first with the reactor charged with cobalt catalyst (X) andthe second with the reactor charged with iron catalyst (A).

TABLE 1 Run No. (l (2) Catalyst Cobalt (X) lron (A) Particle size 118in. pills 8-14 mesh crushed Catalyst weight 400 gm. 439 gm. Reactorpressure 340 atm. 340 atm. Flow direction up flow up flow Reactor BedTemperatures Inlet 98C. -1 10C. Mid point 131C. 121145C. Top 134-142C.142-145C. Feed Rates Adiponitrile 485 grn/hr. 416-471 gin/hr.

NH; 3115 g n/hr. 2470-2735 gm/hr. H, 79 std. ftlhr. 77-84 std.ft-"/hr.Product Analysis (Molar Composition) Hexamethylene diamine 96.4% 98.8%Over conversion products 1 2% 0.8% Under conversion products 1.7% 0Other 0.7% 0.4% Productivity lbJhr. diamine produced per cu. ft. ofcatalyst 148 135447 Total weight of Adiponitrile fed-through put 8800gm. 51000gm. Catalyst activity at end of run low high These resultsindicate that a significant increase in hexamethylenediamine yield andin catalyst life as measured by throughput at the same productivity isattained by the use of iron catalyst instead of cobalt catalyst.

EXAMPLE 2 A variety of reduced iron oxide catalysts was evaluated toshow that the performance observed with the iron catalyst of Example 1may be maintained with different species all of which were fused. Theconditions used and results obtained from pilot plant evaluations aregiven below:

TABLE 2 Run No. (1) (2) (3) Iron Catalyst A B C Particle size-crushed8X14 mesh 8X14 mesh 8X14 Catalyst weight 439 gm. 385 gm. 51 1 gm.Reactor pressure 340 atm. 340 atm. 340 atm. Flow direction up flow upflow up flow Reactor Bed Temperatures Inlet 105-110C 107-117C 108- 1 19CMid point 121-145C lilo-158C 125- 182C Top 142-145C |45-155C 148- 162CFeed Rates Adiponitrile 416-471 397-515 436-561 gm/hr. gm/hr. gin/hr. NH2470-2735 2169-3252 2350- gm/hr. gm/hr. 3038 gm/hr. 1-1 77-84 std. 72-74std. 81-87 cuft/hr. cu.ft/hr. std.

cu. ft/ hr. Product Analysis Hexamethylene diamine 98.8% 97.7% 97.7%Over Conversion products 0.8% 0.8% 0.5% Under Conversion products 0 00.1% Others 0.4 ll: 1.5% 1.7% Productivity lh/hr. diamine produced percult. of catalyst 135-147 121-159 133-163 Total Weight of adiponitrilefed-throughput 51000 gm. 40500 gm. 43300 gm Catalyst activity at end ofrun high high high The 1.1 percent difference in hexamethylene diamineyield indicated between Run 1) and the other two Runs results from thepresence of 0.2 percent water in the ammonia used in the other two Runs.in Run (1) the water content of the ammonia was less than 0.01 percent.Catalyst (B) used in the above Example was a catalyst similar toCatalyst (A) except that it contained 5 percent by weight of alumina.Catalyst (C) used in the above Example was obtained by activating aniron oxide occuring naturally in Labrador.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A process for the catalystic hydrogenation of adiponitrile in thesuper-critical vapor phase to hexamethylene-diamine at a temperaturewithin the range of C. to 200C. under superatmospheric pressures in thepresence of ammonia and a catalyst comprising substantially elementaliron in granular form, prepared by contacting an iron compound withhydrogen at temperatures not exceeding 600C.

2. The process of claim 1 wherein the iron compound from which thecatalyst is prepared is an oxide of iron.

3. The process of claim 2 wherein the oxide of iron contains arefractory oxide.

. The process 0 claim 2 wherein the catalyst has been prepared bycontacting the oxide of iron with hydrogen at a temperature between250C. and 550C.

5. The process of claim 4 wherein the catalytic hydrogenation reactionis conducted between C. and C.

6. The process of claim 5 wherein the catalytic hydrogenation reactionis conducted at a pressure of about 340 atmospheres.

7. The process of claim 1 wherein the iron compound is an oxide of iron,which has been d with carbon monoxide at a temperature ranging from250C. to 450 C. for a time sufficient to produce substantial amounts ofiron carbide, prior to contacting with hydrogen.

P040541 UNITED STATES 'EATENT OFFICE- QERTEFIQATE 0F (JORREfiTION PatentNo. 3. 9 53 Dated October 3, 97

Inventofls) Bernard John Kershaw; Maurice George Founder;

Kenneth Ross Wilkins It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

r- "1 Column 6, line 1 4-, "catalystic" should read --catalytic--; line36, "d" should read --trea.ted-.

Signed and sealed this 3rd day of July 1973.

(SEAL) Attest:

EDWARD M.FLET( IHER,JR. Rene Tegtmeyer Attesting Offlcer ActingCommissioner of Patents

2. The process of claim 1 wherein the iron compound from which the catalyst is prepared is an oxide of iron.
 3. The process of claim 2 wherein the oxide of iron contains a refractory oxide.
 4. The process of claim 2 wherein the catalyst has been prepared by contacting the oxide of iron with hydrogen at a temperature between 250*C. and 550*C.
 5. The process of claim 4 wherein the catalytic hydrogenation reaction is conducted between 105*C. and 165*C.
 6. The process of claim 5 wherein the catalytic hydrogenation reaction is conducted at a pressure of about 340 atmospheres.
 7. The process of claim 1 wherein the iron compound is an oxide of iron, which has been d with carbon monoxide at a temperature ranging from 250*C. to 450* C. for a time sufficient to produce substantial amounts of iron carbide, prior to contacting with hydrogen. 